Electrochemical sensor and method of using same

ABSTRACT

A chemical sensor may include an electrode array for electrically interfacing with a fluid sample. The sensor can apply an electrical potential to the sample in order to effect a current flow within the sample. The sensor can measure the resulting current through the sample and determine characteristics about the fluid sample from the current measurement. In one mode of operation of the sensor, the applied electrical potential can be controlled to cause desired electrochemical reactions, such as oxidation or reduction, to occur within the sample to determine the concentration of the oxidized or reduced sample constituent. In another mode of operation, the applied electrical potential causes a current to flow simply due to the conductivity of the sample. In various embodiments, the sensor comprises a controller and a switch for switching between various modes of operation and applying appropriate electric potentials to the sample.

TECHNICAL FIELD

This disclosure relates generally to electrical measuring devices and,more particularly, to multi-electrode probes and other integratedsensors for monitoring the concentration of one or more substances in asample.

BACKGROUND

In cleaning and antimicrobial operations, commercial users (e.g.,restaurants, hotels, food and beverage plants, grocery stores, etc.)rely upon the concentration of a cleaning or antimicrobial product tomake the product work effectively. Failure of a cleaning orantimicrobial product to work effectively (for example due toconcentration issues) can cause a commercial user to perceive theproduct as lower quality. End consumers may also perceive the commercialprovider of such products as providing inferior services. In addition,commercial users may be investigated and/or sanctioned by governmentregulatory and health agencies. Accordingly, there is a need for asystem that can monitor the characteristics of fluid solutions, e.g., todetermine if the concentration of a product is within a specifiedconcentration range. The same may be true for other applications, suchas commercial and industrial water treatment, pest control, beverage andbottling operations, oil and gas refining and processing operations, andthe like.

One method of monitoring the concentration of a product relies onelectroanalytical methods to measure various parameters of the product.One such parameter can be the conductivity of the product. Some existingconductivity sensors comprise two electrodes, and operate by applying avoltage across the two electrodes and measuring a resulting current. Therelationship between the magnitudes of the current and the voltage allowthe resistance and therefore conductivity of the product to bedetermined. Such two-electrode designs can result in fouling effects atthe electrodes and/or narrow ranges of operation.

More expensive four-electrode devices have been used to overcome some ofthe shortcomings of the two-electrode designs. Exemplary four-electrodedevices can pass a current from one electrode to another to maintain acertain voltage between two separate electrodes. Other devices pass aknown current between two of the electrodes and measure the voltagedifference between the other two electrodes. One disadvantage of suchdesigns, however, is that in some cases, such as in the case of highproduct resistance, the device must apply an undesirably high voltage inorder to achieve an appropriate current. High voltages can causeelectrode polarization, unwanted electrochemical reactions within thesample, and fouling of the electrodes.

SUMMARY

In general, this disclosure is related to a sensor, a system comprisinga sensor, and a method for analyzing a fluid sample. In some examples, asensor includes first and second operational amplifiers and an electrodearray having first, second, third and fourth electrodes. In variousembodiments, the electrodes can be mounted in a first face of anon-conductive housing of the sensor. Electrodes can be arrangedlinearly, and can be positioned such that the distance between each pairof adjacent electrodes is substantially the same. In some embodiments,the first electrode is coupled to the output of the first operationalamplifier, the second electrode is coupled to the input of the firstoperational amplifier, and the third electrode is coupled to theinverting input of the second operational amplifier. The sensor caninclude a switch comprising a first and second position and coupled tothe output of the second operational amplifier. In the first position,the switch couples the output of the second operational amplifier to thefourth electrode, and in the second position, the switch couples theoutput of the second operational amplifier to the third electrode. Theswitch can be positioned into the first or second position depending onthe desired mode of operation of the sensor.

The sensor can include a sense resistor coupled between either theoutput of the first operational amplifier and the first electrode orbetween the output of the second operational amplifier and the switch.The sensor can include a differential amplifier configured to output anelectrical signal corresponding to a current flowing through the senseresistor. For example, the differential amplifier can be configured tomeasure the voltage drop across the sense resistor while a current flowstherethrough. The output of the differential amplifier in such aconfiguration corresponds to the current flowing through the senseresistor. Because of the location of the sense resistor (i.e., betweenthe low-impedance outputs of the first and second operationalamplifiers), current flow through the sample from the sensor will flowthrough the sense resistor, and therefore can be measured via thedifferential amplifier.

The sensor can be part of a system including a controller and aninterface. One or both of the controller or interface can be integratedinto the housing of the sensor. In some embodiments, a user can select amode of operation of sensor via the interface. Selecting a mode ofoperation can include selecting a conductivity mode or anelectrochemical mode. The switch may be placed in one of its first orsecond positions based on the selected mode of operation. Inconductivity mode, an electrical potential can be applied across thesample via the electrode array. The conductivity of the sample causes acurrent to flow therethrough based on the applied potential. Thus, witha known applied potential and a measured resultant current, theconductivity of the sample, and in some embodiments, the combinedconcentration of ionized and soluble species, can be determined. Thesensor can include switching means configured to direct current throughthe sample in a particular direction. Switching means can be switched ata particular frequency to provide a substantially AC potential to thesample, or can be set in a single direction to provide a DC potential tothe sample. In electrochemical mode, the user can select a targetconstituent of the sample to analyze. An appropriate redox potential canbe applied to the sample via the electrode array to initiate a redoxreaction within the fluid sample. Current flow triggered by the redoxreaction can be used to determine the concentration of the targetconstituent within the sample. Exemplary target constituents to beoxidized or reduced include peroxides, peracids and hypochlorite.

In either mode of operation, the controller can be configured to controlthe electrical potential applied to the sample, determine the currentflowing through the sample, and determine the desired parameter from thedetermined current. Some additional parameters, such as the sampletemperature, can have an effect on the relationship between the measuredcurrent and the desired sample parameters. As such, in some embodiments,additional sensors can be included in the housing of the sensor. Forexample, a temperature sensor can be disposed in one of the electrodesand placed in thermal contact with the sample via the electrode. Thesensor can also include a lens for emitting light into and receivinglight from the sample to perform additional analysis.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example fluid system that mayinclude a chemical sensor according to examples of the disclosure.

FIG. 2 is a view of an exemplary chemical sensor disposed in a fluidsample.

FIG. 3 is an illustrative example of a first face of a housingcomprising an electrode array.

FIGS. 4A and 4B are a schematic circuit diagrams showing exemplarycircuitry for controlling the chemical sensor.

FIGS. 5A-5D are exemplary plots illustrating measurements using thecircuit of FIGS. 4A and 4B.

FIG. 6 is a cross-sectional view a first face of a housing comprising anelectrode array, taken along line 6-6 in FIG. 3.

FIG. 7 is a view of a temperature sensor disposed in an electrode in anexemplary configuration such as in box 7-7 in FIG. 6.

FIG. 8 is a process flow diagram illustrating exemplary operation of asensor by a user.

FIG. 9 is a process-flow diagram outlining an exemplary method to beperformed by a sensor within a fluid analysis system in accordance withsome aspects of the present invention.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description provides somepractical illustrations for implementing examples of the presentinvention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of ordinary skill inthe field of the invention. Those skilled in the art will recognize thatmany of the noted examples have a variety of suitable alternatives.

Chemical sensors are used in a variety of applications in a variety ofways, including monitoring industrial processes. In some instances, achemical sensor can be implemented as a portable, hand-held device thatis used to periodically analyze, for example, the electricalcharacteristics of a fluid in an industrial process. Alternatively, achemical sensor can be installed online to continuously analyze theelectrical characteristics of a fluid in an industrial process. Ineither case, the chemical sensor may electrically analyze the fluidsample and determine different characteristics of the fluid, such as theconcentration of one or more chemical species in the fluid.

As one example, chemical sensors can be used in industrial cleaning andsanitizing applications. During an industrial cleaning and sanitizingprocess, water is typically pumped through an industrial piping systemto flush the piping system of product residing in pipes and anycontamination build-up inside the pipes. The water may also contain asanitizing agent that functions to sanitize and disinfect the pipingsystem. The cleaning and sanitizing process can prepare the pipingsystem to receive new product and/or a different product than waspreviously processed on the system.

A chemical sensor can be used to monitor the characteristics of flushingand/or sanitizing water flowing through a piping system during anindustrial cleaning and sanitizing process. Either continuously or on anintermittent basis, samples of water are extracted from the pipingsystem and delivered to the chemical sensor. At the chemical sensor,electrical current is directed into and received from the water sampleand the received current and/or related parameters are used to evaluatethe characteristics of the water sample. The chemical sensor maydetermine whether residual product in the piping system has beensufficiently flushed out of the pipes, for example, by determining thatthere is little or no residual product in the water sample. The chemicalsensor may also determine the concentration of sanitizer in the watersample, for example, by measuring the electrical conductivity of thesample or by measuring an electrochemical response by the sanitizer inresponse to the electrical current emitted into the water sample. If itis determined that there is an insufficient amount of sanitizer in thewater sample to properly sanitize the piping system, the amount ofsanitizer is increased to ensure proper sanitizing of the system.

While such a chemical sensor for analyzing electrical characteristics ofa fluid can have a variety of different configurations, in someexamples, the chemical sensor is designed to have an electrode array viawhich electrical current is emitted into a fluid sample and alsoreceived from the fluid sample. Electrodes in the electrode array cancomprise any electrically conductive material, but care should be takento ensure that the electrode material does not react unfavorably withthe fluid sample to be analyzed. The chemical sensor may include ahousing that contains various electronic components of the sensor tointerface with the electrode array and the sample. The housing can bedesigned to be readily installed through a variety of mechanical pipeand process fittings to electrically analyze a desired process fluid.

FIG. 1 is a conceptual diagram illustrating an example fluid system 100,which may be used to produce a chemical solution having electricalproperties, such as a sanitizer solution exhibiting certain electricalconductivity and/or electrochemical properties. Fluid system 100includes chemical sensor 102, a reservoir 104, a controller 106, and apump 108. Reservoir 104 may store a concentrated chemical agent that canbe blended with a diluent, such as water, to generate the chemicalsolution, or can be any other source for the sample to be characterized.Chemical sensor 102 is electrically coupled to fluid in fluid pathway110 and can be configured to determine one or more characteristics ofthe solution traveling through the fluid pathway. Coupled, as usedherein, can include being directly attached or adjoined by interveningelements.

The fluid pathway 110 can be a single fluid vessel or combination ofvessels which carry a fluid sample through the fluid system 100including, but not limited to, pipes, tanks, valves, pipe tees andjunctions, and the like. In some instances, one or more components ofthe fluid pathway 110 can define an interface or opening sized toreceive or otherwise engage with the chemical sensor 102. In operation,chemical sensor 102 can communicate with controller 106, and controller106 can control fluid system 100 based on the fluid characteristicinformation generated by the chemical sensor.

Controller 106 is communicatively connected to chemical sensor 102 andpump 108. Controller 106 includes processor 112 and memory 114.Controller 106 communicates with pump 108 via a connection 116. Signalsgenerated by chemical sensor 102 are communicated to controller 106 viaa wired or wireless connection, which in the example of FIG. 1 isillustrated as wired connection 118. Memory 109 stores software forrunning controller 106 and may also store data generated or received byprocessor 112, e.g., from chemical sensor 102. Processor 112 runssoftware stored in memory 114 to manage the operation of fluid system100.

As described in greater detail below, chemical sensor 102 is configuredto analyze electrical properties of a sample of fluid flowing throughfluid pathway 110. Chemical sensor 102 may include an electrode arrayconfigured to interface with the fluid sample and to provide electricalcurrent thereto and receive electrical current therefrom. The sensor 102can include electrical components configured to receive feedback signalsfrom the fluid sample to govern electrical operation of the sensor 102.

Independent of the specific composition of the fluid generated by fluidsystem 100, the system can generate fluid in any suitable fashion. Underthe control of controller 106, pump 108 can mechanically pump a definedquantity of concentrated chemical agent out of reservoir 104 and combinethe chemical agent with water to generate a liquid solution suitable forthe intended application. Fluid pathway 110 can then convey the liquidsolution to an intended discharge location. In some examples, fluidsystem 100 may generate a flow of liquid solution continuously for aperiod of time such as, e.g., a period of greater than 5 minutes, aperiod of greater than 30 minutes, or even a period of greater than 24hours. Fluid system 100 may generate solution continuously in that theflow of solution passing through fluid pathway 110 may be substantiallyor entirely uninterrupted over the period of time.

In some examples, monitoring the characteristics of the fluid flowingthrough fluid pathway 110 can help ensure that the fluid isappropriately formulated for an intended downstream application.Monitoring the characteristics of the fluid flowing through fluidpathway 110 can also provide feedback information, e.g., for adjustingparameters used to generate new fluid solution. For these and otherreasons, fluid system 100 can include a sensor to determine variouscharacteristics of the fluid generated by the system. The sensor canengage directly with the fluid pathway 110 to monitor fluidcharacteristics, or can alternatively receive fluid from the fluidsystem 100 separately from the fluid pathway 110.

In the example of FIG. 1, fluid system 100 includes chemical sensor 102.The chemical sensor 102 can engage the fluid pathway 110 in any numberof ways, such as interfacing with a tee configuration in a pipe in thefluid pathway 110, being inserted into a port of a tank or other fluidvessel through which fluid periodically flows, or the like. Chemicalsensor 102 may utilize components thereof to determine one or morecharacteristics of the fluid flowing through fluid pathway 110. Examplecharacteristics include, but are not limited to, the concentration ofone or more chemical compounds within the fluid (e.g., the concentrationof one or more active agents added from reservoir 104 and/or theconcentration of one or more materials being flushed from piping influid system 100), the temperature of the fluid, optical properties suchas the fluorescence and/or turbidity of the fluid, the electricalconductivity of the fluid, the pH of the fluid, the flow rate at whichthe fluid moves through past the chemical sensor, and/or othercharacteristics of the fluid that may help ensure the system from whichthe fluid sample being analyzed is operating properly. Chemical sensor102 may communicate detected characteristic information to controller106 via connection 118.

Chemical sensor 102 may be controlled by controller 106 or one or moreother controllers within fluid system 100. For example, chemical sensor102 may include a device controller (not illustrated in FIG. 1) thatcontrols the chemical sensor to direct electrical current into the fluidunder analysis and also to receive electrical current back from thefluid using the electrode array. The device controller may be positionedphysically adjacent to the other components of the chemical sensor, suchas inside a housing that houses electrical components of the chemicalsensor. In such examples, controller 106 may function as a systemcontroller that is communicatively coupled to the device controller ofchemical sensor 102. The system controller 106 may control fluid system100 based on electrical characteristic data received from and/orgenerated by the device controller. In other examples, chemical sensor102 does not include a separate device controller but instead iscontrolled by controller 106 that also controls fluid system 100.Therefore, although chemical sensor 102 is generally described as beingcontrolled by controller 106, it should be appreciated that fluid system100 may include one or more controllers (e.g., two, three, or more),working alone or in combination, to perform the functions attributed tochemical sensor 102 and controller 106 in this disclosure. Devicesdescribed as controllers may include processors, such asmicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs), orany other equivalent integrated or discrete logic circuitry, as well asany combinations of such components.

In the example illustrated in FIG. 1, processor 112 of controller 106can receive determined electrical characteristic information fromchemical sensor 102 and compare the determined characteristicinformation to one or more thresholds stored in memory 114, such as oneor more concentration thresholds. Based on the comparison, controller106 may adjust fluid system 100, e.g., so that the detectedcharacteristic matches a target value for the characteristic. In someexamples, controller 106 starts and/or stops pump 108 or increasesand/or decreases the rate of pump 108 to adjust the concentration of achemical compound flowing through fluid pathway 110. Starting pump 108or increasing the operating rate of pump 108 can increase theconcentration of the chemical compound in the fluid. Stopping pump 108or decreasing the operating rate of pump 108 can decrease theconcentration of chemical compound in the fluid. In some additionalexamples, controller 106 may control the flow of water that mixes with achemical compound in reservoir 104 based on determined characteristicinformation, for example, by starting or stopping a pump that controlsthe flow of water or by increasing or decreasing the rate at which thepump operates. Although not illustrated in the example fluid system 100of FIG. 1, controller 106 may also be communicatively coupled to a heatexchanger, heater, and/or cooler to adjust the temperature of fluidflowing through fluid pathway 110 based on characteristic informationreceived from chemical sensor 102.

In yet other examples, chemical sensor 102 may be used to determine oneor more characteristics of a stationary volume of fluid that does notflow through a flow chamber of the fluid system. For example, chemicalsensor 102 may be implemented as an offline monitoring tool (e.g., as ahandheld sensor), that requires filling a separate vessel with a fluidsample manually extracted from fluid system 100. The separate vesselcan, in some embodiments, be integrated into the chemical sensor.Alternatively, the chemical sensor 102 can engage a portion of the fluidsystem 100 configured to receive and hold a stationary volume of thefluid, such as a stop-flow device, or an otherwise external vessel forreceiving fluid and engaging the chemical sensor 102. In someembodiments, a controller 106 can control a system of pumps and/orvalves to direct a finite amount of the sample to be measured into sucha stationary vessel outfitted with a sensor 102.

Fluid system 100 in the example of FIG. 1 also includes reservoir 104,pump 108, and fluid pathway 110. Reservoir 104 may be any type ofcontainer that stores a chemical agent for subsequent deliveryincluding, e.g., a tank, a tote, a bottle, and a box. Reservoir 104 maystore a liquid, a solid (e.g., powder), and/or a gas. Pump 108 may beany form of pumping mechanism that supplies fluid from reservoir 104.For example, pump 108 may comprise a peristaltic pump or other form ofcontinuous pump, a positive-displacement pump, or any other type of pumpappropriate for the particular application. In examples in whichreservoir 104 stores a solid and/or a gas, pump 108 may be replaced witha different type of metering device configured to deliver the gas and/orsolid chemical agent to an intended discharge location. Fluid pathway110 in fluid system 100 may be any type of flexible or inflexibletubing, piping, or conduit.

In the example of FIG. 1, chemical sensor 102 determines acharacteristic of the fluid flowing through fluid pathway 110 (e.g.,concentration of a chemical compound, conductivity, temperature or thelike) and controller 106 controls fluid system 100 based on thedetermined characteristic and, e.g., a target characteristic stored inmemory 114. FIG. 2 is a view of an exemplary chemical sensor disposed ina fluid sample. FIG. 2 shows at least a portion of sensor 102 having ahousing 120 and an electrode array 124. Housing 120 can be made from anyappropriate non-conductive material, such as a rubber, plastic, ceramicor the like. The electrode array 124 in FIG. 2 comprises a first 126,second 128, third 130, and fourth 132 electrode, each electricallycoupled to the fluid sample 134. Fluid sample 134 is shown as beingcontained in analysis chamber 136. Analysis chamber 136 can be any typeof fluid container and can be inline or isolated from a fluid system.For example, analysis chamber 136 can represent a tee in a pipe throughwhich a fluid under analysis flows or any part of the fluid pathway 110.Alternatively, analysis chamber 136 can represent an isolated volume ofsuch a sample automatically or manually extracted from the fluid system100.

Electrode array 124 is shown comprising four electrodes. Electrodes126-132 can comprise any electrically conductive material. Exemplaryelectrodes 126-132 can comprise conductive materials that arenonreactive to the fluid sample 134, such as gold, platinum, stainlesssteel or other nonreactive metals or alloys, or carbon-based materialssuch as boron-doped diamond, glassy carbon or graphite. Some electrodescan be designed for use with a specific fluid sample. In someembodiments, electrodes 126-132 are arranged linearly, such that thesecond electrode 128 is positioned along the line between the first 126and fourth 132 electrodes, and the third electrode 130 is positionedalong the line between the second 128 and fourth 132 electrodes. Infurther embodiments, the spacing between each adjacent electrode isequal. That is, the distance between the first 126 and second 128electrodes is the same as the distance between the second 128 and third130 electrodes, and between the third 130 and fourth 132 electrodes.

In general, electrodes 126-132 provide electrical current to and receiveelectrical signals and current from the fluid sample 134. Accordingly,during operation, electrodes 126-132 are placed in electricalcommunication with the fluid sample. Electrical current provided by thechemical sensor 102 can include either direct or alternating currentsproduced by applying voltages to the electrodes. In some configurations,providing a voltage to the sample from a particular electrode can resultin current being provided to the sample via the same electrode.Accordingly, in some configurations, providing a current to the sampleand providing an electrical potential to the sample are equivalent. Insome systems, the nature of the fluid sample and the magnitude of anapplied voltage determine the relationship between the applied voltageand resulting current, for example.

In some embodiments, the housing 120 of the sensor 102 is non-conductiveso that electrodes 126-132 disposed therein are substantiallyelectrically isolated from one another within the sensor 102. Thehousing 120 can include a first face 122 in which the electrode array124 can be mounted. Electrodes 126-132 can be mounted in the first face122 such that the surface of each electrode is flush with the first face122. FIG. 3 is an illustrative example of a first face of a housingcomprising an electrode array. Electrode array 124 is disposed in thefirst face 122 of a housing, and comprises first 126, second 128, third130 and fourth 132 electrodes. Electrodes 126-132 are substantiallyequally spaced along a linear arrangement. During operation, first face122 can be submerged in a fluid sample, enabling electrical contactbetween electrodes 126-132 and the fluid sample. In some embodiments,the first face 122 can include additional components, enablingadditional measurements by the sensor 102. For example, such as is shownin FIG. 3, the first face 122 can include a lens 138 for coupling lightbetween the interior or the sensor 102 and the fluid sample. Lens 138can be configured to emit light from the sensor 102 into the fluidsample, or receive light from the sample and direct it back into thehousing of the sensor 102. In some embodiments, received light can bescattered or fluoresced by the sample in response to light directed tothe sample via lens 138.

The housing 120 of the sensor 102 can further include circuitry forcontrolling the electrical signals sent to the fluid sample via theelectrode array 124. FIG. 4A is a schematic circuit diagram showingexemplary circuitry for controlling the chemical sensor. The circuitryof FIG. 4A includes first 140 and second 142 operational amplifiers,each having inverting and non-inverting inputs and an output. In someembodiments, the non-inverting input of each operational amplifier iscoupled to a switching mechanism 144, which effectively couples one ofthe non-inverting inputs to a voltage source 146 and the othernon-inverting input to voltage source 148. In the illustratedembodiment, voltage source 146 is shown as having a voltage value of Vi,while voltage source 148 is shown as being 0V (ground).

It will be appreciated that these values are exemplary and are shown assuch for the purposes of describing aspects of the operation of theinvention. In general, voltage sources 146 and 148 can output anyarbitrary voltages that provide an appropriate voltage differencetherebetween. As such, in some embodiments, the operational amplifierreceiving a voltage at its non-inverting input from voltage source 146is defined as the powered amplifier, while the operational amplifierreceiving a voltage at its non-inverting input from voltage source 148is defined as the reference amplifier. These terms are not limiting, butrather are intended to illustrate that one (powered) amplifier canreceive a voltage that is some defined amount above or below a referencevoltage applied to the other (reference) amplifier. “Vi” and “ground,”are used in the illustrated embodiments and throughout the descriptionmerely to indicate a voltage difference of Vi, and should not be seen aslimiting.

Switching mechanism 144 and the voltage source 146 can be controlled bya controller 155. While shown as controlled by a single controller 155,switching mechanism 144 and voltage source 146 can be controlled byseparate controllers. In some embodiments, controller 155 can include,be included in, or otherwise communicate with system controller 106shown in FIG. 1. In the illustrated embodiment of FIG. 4A, switchingmechanism couples the non-inverting input of the first operationalamplifier 140 to the voltage source 146 at voltage Vi and thenon-inverting input of the second operational amplifier 142 to ground148. The switching mechanism can switch which non-inverting input iscoupled to the voltage source 146 and which is coupled to ground 148 ata predetermined frequency, effectively producing AC square waves at eachnon-inverting input, 180 degrees out of phase with one another.

The diagram of FIG. 4A shows an exemplary arrangement of the electrodesin the electrode array 124. As shown, the first electrode 126 is coupledto the output of the first operational amplifier 140 and the secondelectrode 128 is coupled to the inverting input of the first operationalamplifier 140. The output of the second operational amplifier 142 can becoupled to the input of a switch 133 with outputs coupled to the third130 (position E) and fourth 132 (position C) electrodes. In someembodiments, the switch 133 can be in communication with controller 155.The third electrode 130 can be additionally coupled to the invertinginput of the second operational amplifier 142. In the configuration ofFIG. 4A, switch 133 is in position C, connected to output to the fourthelectrode 132, and each electrode 126-132 is shown as being disposed ina fluid sample 134.

The fluid sample 134 has associated with it an electrical conductivity.Accordingly, a distance between two points has associated with it anelectrical resistance. In the illustrated embodiment, electrodes 126-132are evenly spaced apart, and so the electrical resistance between eachpair of adjacent electrodes is generally equal. The resistance of thefluid sample 134 between adjacent electrodes is shown schematically by aresistor illustrated in dotted lines and labeled Rs. It will beappreciated that alternative configurations are possible in which theelectrodes need not be spaced equally apart. Linearly arrangedelectrodes of a known spacing can be used and, since the resistancebetween electrodes is proportional to the distance between them,relationships between unequal resistances can be determined from theknown spacing of electrodes.

An arrangement such as that shown in FIG. 4A can be used, for example,to determine the electrical conductivity of a fluid sample. In anexemplary operation, the non-inverting input of the first operationalamplifier 140 is coupled to voltage source 146 and held at voltage Viwhile the non-inverting input of the second operational amplifier 142 iscoupled to ground. First operational amplifier 140 will operate suchthat it will output an electrical signal in an attempt to producevoltage Vi at the inverting input of the amplifier 140, coupled to thesecond electrode 128. Similarly, the second operational amplifier 142will operate to hold the inverting input of the amplifier 142, which iscoupled to the third electrode 130, at ground. Accordingly, the first140 and second 142 operational amplifiers will act to produce a voltagedifferential of Vi between the second 128 and third 130 electrodes. Inthe illustrated embodiment, the resistance between these electrodes isshown as Rs. By Ohm's law, a voltage drop Vi over resistance Rs suggestsa current of I=Vi/Rs is flowing through the solution between the second128 and third 130 electrodes in the direction of arrow 149. Becauseoperational amplifiers tend to have very high input impedances, thiscurrent is not produced by the inverting inputs coupled to the second128 and third 130 electrodes. Rather, the first 140 and second 142operational amplifiers output an appropriate signal to create such acurrent.

Since current flows through the system in the direction of arrow 149,and cannot flow into or out of inputs of the operational amplifiers(i.e., second 128 and third 130 electrodes), current must flow throughthe system from the output of the first operational amplifier 140,acting as a current source, to the output of the second amplifier 142,acting as a current sink. Analogously, current flows into the fluidsample 134 via the first electrode 126, through the fluid sample 134,and out of the fluid sample 134 via the fourth electrode 132. In someembodiments, a sense resistor 150 of a known resistance R is disposedbetween the output of the first operational amplifier 140 and the firstelectrode 126. In some exemplary embodiments, R is 33Ω. The voltage dropacross the sense resistor 150 can be measured by means known in the art.In the illustrated embodiment, a differential amplifier 152 ispositioned with inputs on either side of the sense resistor 150.Differential amplifier 152 is arranged to provide an outputcorresponding to the difference in voltage received at its inputsignals. In this configuration, the difference in input signals will bethe voltage drop across sense resistor 150. The output V′ ofdifferential amplifier 152 can be measured by a meter 154. In someembodiments, the output of a meter 154 or differential amplifier 152 canbe communicated to controller 155.

From the measurement of the output voltage V′ of the differentialamplifier 152, the voltage drop V across the sense resistor 150 can bedetermined from known amplifier parameters. Combined with the knownresistance R of the sense resistor 150, the current flowing through thesense resistor 150 can be determined: I=V/R. Because current is flowingin a single loop in the system (from first operational amplifier 140through sense resistor 150 to the first electrode 126, from the firstelectrode 126 into the fluid sample 134, through the fluid sample 134 tothe fourth electrode 132, and from the fourth electrode 132 throughswitch 133 to the second operational amplifier 142), the current throughthe sense resistor 150 is substantially the same as the current throughthe fluid sample 134. That is: V/R=I=Vi/Rs; or V/R=Vi/Rs. Because Vi isa known applied voltage, R is a known resistance, and the voltage drop Vacross the sense resistor 150 can be determined from the measurement ofV′ from the differential amplifier 152, Rs can be solved for: Rs=R×Vi/V.The resistance Rs of the fluid sample 134 can be used in conjunctionwith known dimensions of the electrode array 124 in order to calculatethe conductivity of the fluid sample 134. In some embodiments,controller 155 can determine sample conductivity using the output of themeter 154. In one example, controller 155 can utilize preprogrammeddimensions of the electrode array 124 along with a known appliedpotential Vi from voltage source 146 to calculate the sampleconductivity. In a second example, controller 155 can determine theconductivity of the sample from a lookup table stored in memory. Lookuptable can, in some examples, be generated by running conductivitycalibration standards.

During conductivity measurements, the difference between voltage sources146 and 148, represented as Vi, is kept generally low so as to notinduce electrochemical corrosion that can damage the electrodes. Largervoltages can cause electrochemical reactions in the fluid sample 134that can be damaging to the electrodes or alter the fluid sample 134itself. In some embodiments, Vi is between 0.1 and 0.3 volts, and infurther embodiments, Vi can be adjustable on the fly from a low to ahigher voltage. In such cases, Vi can be adjusted in response to theconductivity range of the sample 134. For example, a more conductivesample (i.e., a sample having a lower resistance Rs) can be analyzedwith a lower value of Vi than can a less conductive sample. In addition,switching mechanism 144 can act to alternate the direction of currentflow in the sample 134. When the non-inverting input of the secondoperational amplifier 142 is tied to the voltage source 146, currentwill flow in the opposite direction when compared to the configurationin which the non-inverting input of the first operational amplifier 140is tied to the voltage source 146. Switching mechanism 144 can alternatewhich non-inverting input is tied to the voltage source 146 while tyingthe other non-inverting input to ground. That is, switching mechanism144 can cycle the non-inverting input of each operational amplifierbetween Vi and ground 180 degrees out of phase with one another. In someembodiments, switching is performed at a sufficiently high rate to avoidelectrode polarization and potentially resulting measurement errors. Insome embodiments, switching is performed at a frequency of at least 1kHz. Switching mechanism 144 can comprise, for example, solid stateswitches controlled by a controller 155.

During operation, switching mechanism 144 can cause an alternatingcurrent to flow through sense resistor 150. Accordingly, the voltagedrop across the sense resistor 150 will change sign as the currentchanges direction. In some embodiments, differential amplifier 152comprises a built-in offset, such that the output of the amplifier 152will be above or below the offset value depending on the sign of thesensed voltage drop. In some such embodiments, the voltage V′ from thedifferential amplifier 152 will always be positive, regardless of thedirection of current flow through the sense resistor 150—a voltage dropin one direction will result in an output voltage of a certain valueabove the offset, while a voltage drop in the other direction willresult in an output voltage of a value below the offset. Exemplary datais illustrated in the plot of FIG. 5A, which shows the voltage dropacross the sense resistor R in both directions with relation to theoffset as conductivity of the sample is increased.

In embodiments in which an alternating current voltage is applied fromthe voltage source 146 and the differential amplifier 152 comprises abuilt-in offset, the output voltage V′ from the differential amplifier152 can alternate on either side of the offset voltage. Accordingly, fora given conductivity, the controller 155 will receive two differentoutput voltage signals depending on the direction of current flow. Insome such embodiments, the controller can calculate the differencebetween the two output voltage signals and use the calculated differenceto determine the conductivity of the fluid sample. In using thedifference measurement, both polarities of circuit operation are used.This can average out slight variations due to inhomogeneity in sampleflow or turbulence past the sensor. In addition, the differencemeasurement yields a larger measured voltage for greater precision.

Measurements of the conductivity of a sample can provide informationindicative of a combined concentration of ionized and soluble species ina fluid sample, such as sanitizers, detergents, acids, and bases in anaqueous solution, for example. FIG. 5B is an exemplary plot illustratingthe change in the voltage drop across the sense resistor 150, and thusthe conductivity, with the addition of a conductive constituent such ashypochlorite, peracid, or caustic. In some embodiments, the controllercan determine the sample conductivity and subsequently determine thesample concentration via a lookup table stored in memory, for example.As discussed elsewhere herein, when determining electrical conductivityaccording to methods herein described, the voltage applied to the sampleis kept relatively low in order to prevent unwanted electrochemicalreactions from taking place. However, in some situations, suchelectrochemical reactions can be utilized to provide additionalinformation about the sample.

In some configurations, fluid sample 134 comprises constituents that areelectrochemically active. When a sufficient potential is applied to sucha fluid sample, reduction and/or oxidation reactions can occur. Ingeneral, a sufficiently high potential for causing electrochemicalreactions is such that it creates energetically favorable conditions forelectrons to transfer (i) from the solution to an electrode or (ii) froman electrode to the solution. The applied potential necessary to causethe transfer of charge between an electrode and a particular constituentin the fluid sample (the redox potential), depends on the constituentgaining or losing the electrons. In some examples, electrochemicallyinduced redox reactions can be used to selectively measure peroxides,peracids, and/or hypochlorite. In some embodiments, the redox potentialfor a target constituent is between approximately −0.8V and −1.0V. Insome fluid systems, then, a target constituent with a known redoxpotential can be driven to electrochemical reaction to determine theconcentration of the constituent in the fluid sample.

Such reactions can cause a transfer of charge between the electrodes andthe fluid sample and result in a current flow. For example, two commoncleaning products are hydrogen peroxide and chlorine (bleach). Foracidic peroxide, the electrochemical reduction equation isH2O2+2H++2e−→2H2O. Hydrogen peroxide is reduced to water. For alkalinebleach, electrochemical reduction is OCl—+H2O+2e−→Cl—+2OH—. Herehypochlorite is reduced to chloride. Each of these processes willconduct a flow of current in the sensor when the voltage differential is−0.8V.

During exemplary operation utilizing an electrochemical reaction, switch133 can be set to position E as shown in FIG. 4B, coupling the output ofthe second operational amplifier 142 to the third electrode 130. In sucha configuration, the fourth electrode 132 can be used for a separatemeasurement or can otherwise be left unused. The electrode array 124 ofthe sensor can be disposed in a fluid sample 134 having a targetconstituent with a known redox potential Vr. Once the electrode array124 is disposed in the sample, voltage source 146 is set by controller106 to output Vi=Vr and voltage source 148 is set to 0V (that is,voltage source 148 represents ground). Thus, the non-inverting input ofthe first operational amplifier 140 is held at a voltage Vi=Vr by avoltage source 146 and the non-inverting input of the second operationalamplifier 142 is tied to ground 148. Alternatively, voltage sources 146and 148 can be held at any voltages such the difference therebetween isa redox potential. That is, the voltage source 146 can define and becoupled to the non-inverting input of the powered amplifier, whilevoltage source 148 can define and be coupled to the non-inverting inputof the reference amplifier. For the case of alkaline bleach, forexample, Vi (or the difference in voltages applied to the non-invertinginputs of operational amplifiers 140 and 142) can be set to −0.8V.

During exemplary operation, a known redox potential of a targetconstituent can be applied between the non-inverting inputs of the first140 and second 142 operational amplifiers. The operational amplifiers140 and 142 will act so that the redox potential will be present betweensecond 128 and third 130 electrodes. In embodiments in which electrodes126-132 are arranged linearly and are equally spaced, then as discussedelsewhere herein, the redox potential will be present between the first126 and second 128 electrodes.

As the redox potential is applied across various electrodes disposed inthe fluid sample 134, if it is energetically favorable for the targetconstituent of the fluid sample 134 to lose electrons (oxidation) orgain electrons (reduction), then target constituent molecules proximatethe third electrode 130 can either give electrons to or gain electronsfrom the third electrode via the output of the second operationalamplifier 142. In some embodiments, redox reactions can occur proximatethe first electrode 126, with electrons being lost or gained therefromvia the output of the first operational amplifier 140. Because thesecond electrode 128 is coupled to the high-impedance inverting input ofthe first operational amplifier 140, constituents of the fluid sample134 cannot lose electrons to or gain electrons from the second electrode128. However, because the first electrode 126 is coupled to the outputof the first operational amplifier 140 and third electrode 130 iscoupled to the output of the second operational amplifier 142 via switch133, electrons can be transferred between first 126 and third 130electrodes and the fluid sample 134.

For example, in an exemplary reduction reaction, a target constituentmolecule proximate the third electrode 130 gains an electron from thethird electrode 130 (by way of the low impedance output of the secondoperational amplifier 142 and switch 133). In order to maintainappropriate potentials and to complete the circuit, the firstoperational amplifier 140 can inject current into the fluid sample 134via its output and the first electrode 126. That is, electrons will beemitted into the fluid sample 134 via reduction of a target constituentat the third electrode 130 and will be extracted via the first electrode126. This flow of electrons creates a current path flowing from theoutput of the first operational amplifier 140 to the first electrode126, through the fluid sample 134, and to the output of the secondoperational amplifier 142 via third electrode 130 and switch 133.

Thus, in oxidation or reduction reactions, the transfer of charge due tothe electrical potentials maintained in the fluid sample and theresultant electrochemical reactions can create an electrochemicalcurrent flowing through the fluid sample 134 from the first electrode126 to the third electrode 130 (i.e. from the output of the firstoperational amplifier 140 to the output of the second operationalamplifier 142). In some embodiments, as charge is depleted/acquired onfirst 126 and/or third 130 electrodes, the second electrode 128 canprovide feedback from the fluid sample 134 to first 140 operationalamplifier, which acts to source and sink current to maintain desiredvoltages throughout the system, such as, in some exemplary embodiments,the redox potential between the second 128 and third electrodes 130. Insome embodiments, at a steady state, first operational amplifier 140provides current through the first electrode 126 to the sample 134,through the sample 134 to the third electrode 130, and from the thirdelectrode 130 to the output of the second operational amplifier 142 viaswitch 133. In other embodiments, current can flow in the oppositedirection through the fluid sample 134.

Because the electrochemical current results from the electrochemicaloxidation or reduction of a target constituent, the magnitude of theelectrochemical current is related to the concentration of the targetconstituent proximate the electrodes. Accordingly, in some embodiments,a sense resistor 150 is disposed between the output of the firstoperational amplifier 140 and the first electrode 126, for example. Asdescribed elsewhere herein, the current flowing through the senseresistor 150 can be measured as a voltage drop from which the currentflowing through the sample can be determined. The concentration of thetarget constituent can then be determined from the determined current.This is illustrated, for example, in FIG. 5C, which is an exemplary plotof the voltage drop across the sense resistor 150 as constituent isadded to the fluid sample during electrochemical operation. While shownin FIGS. 4A and 4B as disposed between the output of the firstoperational amplifier 140 and the first electrode 126, the senseresistor 150 can be positioned at any point in the current path (i.e.,between the outputs of the first 140 and second 142 operationalamplifiers) where the voltage drop thereacross can be measured. Forexample, in some embodiments, the sense resistor 150 can be coupledbetween the output of the second operational amplifier 142 and switch133 while maintaining its functionality and operability.

In some embodiments, during the electrochemical process, the currentflowing through the system can be largely attributed to theelectrochemical reaction of the target constituent. The current causedby the electrochemical reaction is a measurement of the amount of chargeper time received or given by the target constituent. In someembodiments, current additionally flows through the fluid sample 134simply due to the sample's conductivity. However, often this current ismuch smaller than the electrochemical current and can be neglectedand/or can be determined and subtracted from the measuredelectrochemical current.

In some embodiments, the sensor can be used to determine the sampleconductivity with the switch 133 in position C as shown in FIG. 4A,coupling the output of the second operational amplifier 142 to thefourth electrode 132. Determination of the conductivity can be performedas described herein with regard to FIG. 4A. The switch 133 can beadjusted to position E as shown in FIG. 4B and an electrochemicalmeasurement can be performed as described herein with regard to FIG. 4B.The measured conductivity of the fluid sample 134 can be used in anelectrochemical concentration calculation, for example by subtractingany current expected to be flowing through the sample due to the voltagedrop between electrodes across the conductive sample. In someembodiments, the conductivity and/or the concentration measurements andcalculations are controlled by controller 155. In some configurations,controller 155 can perform a conductivity measurement, flip switch 133,perform a concentration measurements, and use the conductivitymeasurement in determining the concentration automatically.

Accordingly, switch 133 can be used to define the mode of operation ofthe controller. A user can position switch 133 in a first position(e.g., position C) or a second position (e.g., position E) forperforming various methods of analysis, such as conductivity orelectrochemical analysis. In some embodiments, user can position theswitch via interface 156, which causes controller 155 to position theswitch appropriately. The controller 155 can automatically positionswitch 133 in response to a command from a user to perform a particularmeasurement.

It should be noted that charge will generally not be transferred to orfrom the second electrode 128, since it is coupled to the high-impedanceinverting inputs of the first operational amplifier 140. As such,fouling effects will not affect operation of the system at secondelectrode 128. First 126 and third 130 electrodes may be subject tofouling effects, however, in some embodiments, changes in sensoroperation due to fouling, such as a change in applied voltage to effectthe same current flow or electrochemical reaction, can provideinformation useful for detecting fouling on the sensor.

As discussed, the fluid sample 134 can be analyzed in line with a fluidsystem or can be isolated and analyzed independently. The fluid sample134 can be analyzed while flowing or non-flowing in either case. When aflowing sample is used, fresh sample flows to the electrodes 126-132throughout the analysis, and the electrochemical current will remainrelatively constant. However, in embodiments in which a non-flowingsample is being analyzed, as the target constituent molecules proximatethe electrodes undergo oxidation or reduction reactions, the remainingtarget constituent available to react can become depleted. As such, overtime, the current flowing caused by the electrochemical reactionsdiminishes because of a lack of available target constituent. Theprocess then becomes limited by diffusion of the target constituentthrough the fluid sample 134. Once the process is entirely limited bydiffusion, the electrochemical reactions and current flow reach a steadystate that is lower than that in the flowing sample. This can be seen,for example, in the exemplary plot of FIG. 5D, in which the measuredvoltage across the sense resistor 150, which is indicative of thecurrent flowing in the sample, decreases over time when a sample isstagnant and no constituent is added.

In some embodiments, the electrochemical current data can be analyzed todetermine the concentration of the target constituent. For example,integrating the current over time results in a calculation of totalcharge transferred over an amount of time. The total charge can beproportional to the number of molecules of target constituent that haveelectrochemically reacted, from which a concentration can be calculated.In some alternative embodiments, relationships between detected currentand the concentration of a target constituent can be stored in a lookuptable.

As has been described, various sample properties are utilized by thesensor to determine others. For example, in the case of non-flowingsamples, the diffusion of a target constituent within a fluid sample canaffect the rate of electrochemical reactions, which can in turn be usedto determine the concentration of the target constituent. However, thediffusivity of a constituent through the sample fluid is not necessarilyconstant with temperature. Temperature dependence of various parameterscan affect the outcome of measurements by the sensor, leading toinaccuracy in measurement.

In some embodiments, the sensor comprises a temperature sensor fordetermining the temperature of the fluid sample. FIG. 6 is across-sectional view a first face of a housing comprising an electrodearray, taken along line 6-6 in FIG. 3. FIG. 6 shows first 126, second128, third 130 and fourth 132 electrodes extending through the firstface 122 of the housing 120. In the illustrated embodiment, electrodes126-132 are flush with the first face 122. Lens 138 is shown protrudingfrom first face 122. In the embodiment of FIG. 6, the first electrode126 comprises a bore 160 extending from a back surface of the firstelectrode 126 toward the first face 122. In some configurations, bore160 can be shaped like an annular tube and be configured to house atemperature sensor 158, for example.

Temperature sensor 158 can be inserted into a bore 160 in the firstelectrode in order to measure the temperature of the fluid sample. Insome embodiments, bore 160 extends only partially through the firstelectrode 126 and does not allow the temperature sensor 158 to contactthe fluid sample directly. Instead, in some configurations, the firstelectrode 126 acts as the thermal conductor, in which the firstelectrode 126 is in thermal equilibrium with the fluid sample and thetemperature sensor 158 measure the temperature of the fluid sample viathe first electrode 126. Preventing contact between the temperaturesensor 158 and the fluid sample can act to reduce wear or corrosion ofthe temperature sensor 158 by the fluid. In such configurations,embedding the temperature sensor in an electrode eliminates therequirement of an additional sealing surface on the sensor face 122.Temperature sensor 158 can include thermistors, thermocouples,resistance temperature detectors (RTD's), such as platinum RTD's,semiconductor temperature devices, or any other known temperaturesensor. In some embodiments, when temperature sensor is an electricalsensor, preventing contact between the temperature sensor 158 and thefluid sample can act to electrically isolate the temperature sensor 158from the fluid sample.

As shown in FIG. 6, electrodes 126-132 can be electrically coupled tocircuitry (such as that shown in FIGS. 4A and 4B) by wires 159.Generally, wires 159 are shown as having bare ends disposed in the endof each electrode 126-132 opposite the first face 122. It will beappreciated that wires 159 can be electrically coupled to electrodes126-132 in any number of configurations in order to prevent shortcircuiting the electrodes 126-132. In some embodiments, the firstelectrode 126 can include a conductive tab 161 for providing aninterface between circuitry and the first electrode 126 while the firstelectrode 126 comprises a bore 160 for housing a temperature sensor 158.For example, a wire 159 for interfacing with the first electrode 126 canbe embedded or otherwise in electrical communication with the conductivetab 161 on the first electrode 126. It should be appreciated that, whiledescribed in the illustrated embodiment as being incorporated into thefirst electrode 126, temperature sensor 158 can be disposed in a bore160 in any of electrodes 126-132 in order to thermally communicate withthe sample. A more detailed exemplary configuration between thetemperature sensor and one of electrodes 126-132 is shown in FIG. 7.

FIG. 7 is a view of a temperature sensor disposed in an electrode in anexemplary configuration such as in box 7-7 in FIG. 6. FIG. 7 shows afirst electrode 126 including a bore 160 along its longitudinal axis.First electrode 126 has a first end 162 having a surface flush with thefirst face 122 of a non-conductive housing 120. A temperature sensor 158is shown disposed in the bore 160. In the illustrated embodiment, bore160 extends toward the first end 162 of the first electrode 126, butdoes not extend to the surface flush with the first face 122.Temperature sensor 158 is positioned into the bore 160 so as to have atemperature sensing end proximate the first end 162 of the firstelectrode 126. In some embodiments, the bore 160 comprises anelectrically insulating coating 164 to prevent unwanted electricalcommunication between the first electrode 126 and the temperature sensor158. Electrically insulating coating 164 can comprise any appropriatelyinsulating coating known. In some embodiments, the electricallyinsulating coating 164 is thermally conductive so as to place thetemperature sensor 158 in thermal communication with the first electrode126.

During operation, the first face 122 of the sensor housing 120 isdisposed into a fluid sample. First electrode 126 contacts the fluidsample and changes temperature based on the temperature of the fluidsample. In some embodiments, the first end 162 of the first electrode126 reaches thermal equilibrium with the fluid sample. The temperaturesensor 158 disposed in the first end 162 of the first electrode 126 alsoreaches thermal equilibrium with the fluid sample and outputstemperature data indicative of the temperature. In some embodiments, thetemperature sensor 158 is coupled to the controller 155 in order tocommunicate the temperature data thereto. Controller 155 can utilizetemperature data while analyzing data, such as current data in aconductivity or electrochemical measurement, for example, in order toaccount for temperature-dependent parameters such as constituentdiffusion.

Electrochemical and conductivity measurements have been described.Embodiments of the invention include sensors having a first face 122having an electrode array 124 such as shown in FIG. 3. Electrodes126-132 in the electrode array 124 can be coupled to a circuitarrangement as is shown in FIGS. 4A and 4B. Such a configuration allowsthe sensor to perform both conductivity and electrochemical measurementswithout manipulation of the sensor—the same arrangement can be used toperform either measurement. In some embodiments, the system comprises acontroller 155 in communication with various components of the circuitin order to perform such measurements and process data. Embodiments ofthe system can include an interface 156 in communication with thecontroller 155. In some systems, for example, a user can initiateoperation of the sensor, define and/or input parameters of the system,determine the mode of operation of the system, or receive informationfrom the system via the interface 156.

In some embodiments, a user can initiate a fluid sample analysisprocedure via interface 156. For example, a user can initiate aconductivity measurement, causing the controller 155 to communicate tothe voltage source 146 to output an appropriate voltage Vi for aconductivity measurement. In some examples, Vi is between 0.1 and 0.2volts for a conductivity measurement. During operation, the controller155 can cause the switching mechanism 144 to toggle which non-invertinginput is coupled to Vi and which to ground. In an exemplary embodiment,the controller 155 toggles two solid state switches at a frequency of 1kHz, effectively applying a 1 kHz square wave between ground and Vi ateach non-inverting input.

Controller 155 can additionally receive a signal from meter 154indicative of the current flowing through the circuit and the fluidsample 134. In some embodiments, controller 155 can include a processorand memory for analyzing the signal received from meter 154. Controller155 can process the received signal and utilize it to calculate theconductivity of the fluid sample 134. In an exemplary operation, a usercommunicates the resistance value of sense resistor 150 to thecontroller 155 via interface 156, and the controller utilizes theresistance value, the voltage Vi from voltage source 146, the receivedsignal from the meter 154 and other known system parameters to determinethe conductivity of the fluid sample 134. In some examples, varioussystem parameters such as Vi and/or the value of the sense resistor 150can be predetermined during construction of the system with valuespreprogrammed into controller 155. In such an example, a user caninitiate a conductivity measurement via interface 156 and the controller155 performs the measurement from predetermined operations andparameters stored in memory. In some embodiments, a user can select oneor more parameters from a series of predetermined selectable options.After determining the conductivity of the fluid sample 134, in someconfigurations the controller 155 can further determine theconcentration of various constituents in the sample, such as, forexample, the combined concentration of ionized and soluble species inthe fluid sample 134.

In some embodiments, a user can initiate electrochemical analysis of thefluid sample 134. As discussed elsewhere herein, various constituents ofa sample electrochemically react at a variety of redox potentials.Accordingly, a user can select a target constituent having acorresponding known redox potential via the interface 156. In someembodiments, user can select the target constituent from a predeterminedlist. Upon selection, the controller 155 can cause the voltage source146 to output an appropriate voltage to effect electrochemical reactionof the target constituent. An appropriate voltage can be stored inmemory, such as in a lookup table based on the target constituent, forexample. As discussed elsewhere herein, the electrochemical process cancause a current to flow through the fluid sample 134 and sense resistor150. The controller 155 can receive a signal indicative of the flowingcurrent from meter 154, and can use the current data to determine theconcentration of the target constituent in the sample.

Embodiments of the present invention include a method for using a sensorsuch as those herein described. FIG. 8 is a process flow diagramillustrating exemplary operation of a sensor by a user. A user candispose 170 the first face of the sensor housing into a fluid sample tobe analyzed. First face comprises electrodes electrically performingsample analysis. The user can select 172 a mode of operation of thesensor depending on the desired sample analysis. In some configurations,the step of selecting a mode of operation 172 can result in thepositioning of switch 133 as in FIGS. 4A and 4B, enabling conductivityor electrochemical operation depending on the positioning of the switch.

The user can select conductivity 174 mode, and can input 176 anyparameters that need to be defined. As described elsewhere herein, insome embodiments, user can select the value of an electrical potentialapplied to the fluid sample or the potential applied to an input of anamplifier that outputs to the fluid sample. A user may need to input theresistance value of a sense resistor used to measure current flowthrough the fluid sample. After inputting 176 any necessary parameters,a user can initiate 178 operation of the sensor. The user can thenreceive conductivity information 180 from the sensor based on theoperation performed by the sensor. Conductivity information can includethe actual conductivity of the sample, a determined resistance of thesample, the current flowing through the sample or any other informationrelated to the conductivity measurement. In some embodiments, the usercan alternatively or additionally receive concentration information 182from the sensor. Concentration information can include the combinedconcentration of ionized and soluble species such as sanitizers,detergents, acids, and bases within the sample.

In other operations, user may select an electrochemical 184 mode ofoperation. As described elsewhere herein, during electrochemicaloperation, a user can select 186 a target constituent of the fluidsample to analyze. This selection will determine the electrical (redox)potential applied to the fluid sample from the sensor. In some cases,the user can set 186 the redox potential manually. Once the targetconstituent or redox potential is set, the user can initiate 188operation of the sensor, causing the sensor to carry out a predeterminedelectrochemical operation based on the set parameters. After operation,the user can receive concentration information 190 from the sensor.Concentration information can include, for example, a measured currentand/or the concentration of the target constituent in the fluid sample.

Embodiments of the invention include methods performed by a component ofor in communication with the sensor. FIG. 9 is a process-flow diagramoutlining an exemplary method to be performed by a sensor within a fluidanalysis system in accordance with some aspects of the presentinvention. Sensor can receive a command 192 to determine a desiredparameter of a fluid sample. The command can be received from a user viaan interface or an automated system configured to initiate analysis at apredetermined time, for example. The sensor can apply an electricalpotential 194 to the fluid sample via a power electrode in accordancewith the command. The nature of the applied electrical potential candepend on the received command. For example, in a conductivitymeasurement, the sensor can apply a low-magnitude, alternating currentpotential to the sample. During electrochemical analysis, however,sensor may apply a larger-magnitude, direct current potential to thesample. In some embodiments, the potential is applied to the samplerelative to a reference ground applied to the sample at a separateelectrode. In general, the power electrode can comprise either of first126 or fourth 132 electrode.

In some embodiments, the sensor can maintain 196 a substantiallyconstant electrical potential within the sample at a feedback electrode.Maintaining a substantially constant potential can include defining areference ground or other reference potential within the sample. In someexamples, the second 128 and third 130 electrodes can act as feedbackelectrodes for the sensor, which applies the necessary potential to thesample so as to maintain a constant potential at the feedbackelectrodes. Sensor can receive 198 electrical current at a collectionelectrode. Current can flow through the sample and collection electrodeas a result of the applied electrical potential from the powerelectrode. The current detected at the collection electrode can beeither positive or negative. That is, current can be flowing from thesample into the collection electrode, or from the collection electrodeinto the sample. As described with regard to various modes of operation,the collection electrode can comprise either the first electrode 126,the third electrode 130 (in electrochemical operation) or the fourthelectrode 132 (in conductivity operation).

The sensor can receive current information 200 regarding the magnitudeof the current flowing through the sample. In some examples, currentflows through a sense resistor of a known resistance. In some examples,current information can comprise a voltage measured across the resistorwhich can be used to determine the flowing current. The voltage dropacross the sense resistor is amplified by a differential amplifier, forexample. In some embodiments, the sensor can receive fluid sampletemperature information 202 from a temperature sensor. Various sampleparameters that can affect the electrical properties of the fluid samplecan be dependent upon the sample temperature. The sensor can perform acalculation to determine 204 a desired parameters of the fluid sample.Determining 204 can be done based on any or all of the appliedelectrical potential, the received current information and the receivedtemperature information. In various embodiments, desired parameter cancomprise the conductivity of the sample, the concentration of a targetconstituent of the fluid sample, or the combined concentration ofionized and soluble species in a fluid sample, for example.

The exemplary method of FIG. 9 can be carried out, for example, by acontroller as a part of or in communication with the sensor. Controllersmay include processors, such as microprocessors, digital signalprocessors (DSPs), application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs), or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components. In some embodiments, methods such as that illustratedin FIG. 9 can be encoded as instructions programmed in a non-transitorycomputer-readable medium for causing a programmable processor to carryout the method in response to a received command.

Various systems, sensors and methods have been described. Such examplesare non-limiting, and do not define or limit the scope of the inventionin any way. Rather, these and other examples are within the scope of thefollowing claims.

The invention claimed is:
 1. A fluid analysis system including a sensor,the sensor comprising: a non-conductive housing; first and secondoperational amplifier, each having an inverting input, a non-invertinginput, and an output; an electrode array for interfacing with a fluidsample and mounted in a first face of the non-conductive housing, theelectrode array comprising: a first electrode coupled to output of thefirst operational amplifier, a second electrode coupled to the invertinginput of the first operational amplifier, a third electrode coupled tothe inverting input of the second operational amplifier, and a fourthelectrode, the electrode array arranged in a line and configured suchthat the second electrode is between the first electrode and the fourthelectrode, and the third electrode is between the second electrode andthe fourth electrode; a switch coupled to the output of the secondoperational amplifier and comprising a first position and a secondposition, such that in the first position, the switch couples the outputof the second operational amplifier to the fourth electrode; and in thesecond position, the switch couples the output of the second operationalamplifier to the third electrode; a sense resistor coupled betweeneither (a) the output of the first operational amplifier and the firstelectrode or (b) the output of the second operational amplifier and theswitch; a switching mechanism for (i) connecting the non-inverting inputof one of the first operational amplifier and the second operationalamplifier to a first voltage source, defining a powered amplifier, and(ii) connecting the non-inverting input of the other of the one of thefirst operational amplifier and the second operational amplifier to asecond voltage source, defining a reference amplifier; and adifferential amplifier configured to output an electrical signalcorresponding to a current flowing through the sense resistor.
 2. Thesystem of claim 1, further comprising a temperature sensor disposed inand electrically isolated from one of the first electrode, the secondelectrode, the third electrode, or the fourth electrode for measuringthe temperature of a sample proximate the one of the first, second,third and fourth electrodes.
 3. The system of claim 2, wherein the oneof the first electrode, the second electrode, the third electrode, orthe fourth electrode that contains the temperature sensor comprises abore opposite the first face for receiving the temperature sensor. 4.The system of claim 3, wherein the bore does not extend entirely throughthe one of the first electrode, the second electrode, the thirdelectrode, or the fourth electrode that contains the temperature sensor,such that the temperature sensor, when disposed in the bore, is notexposed to the fluid sample when the first face of the sensor isdisposed therein.
 5. The system of claim 1, wherein the separationdistance between each pair of adjacent electrodes in the electrode arrayis substantially the same.
 6. The system of claim 1 wherein the first,second, third and fourth electrodes are flush with the first face of thesensor housing.
 7. The system of claim 1, wherein the first, second,third and fourth electrodes comprise at least one of gold, platinum,stainless steel, boron-doped diamond, glassy carbon or graphite.
 8. Thesystem of claim 1, further comprising a controller in communication withthe sensor for determining at least one parameter of a fluid sample. 9.The system of claim 8, wherein the controller is embedded in the sensorhousing.
 10. The system of claim 9, wherein the controller is configuredto: (i) send control signals to the sensor defining the poweredamplifier and the reference amplifier; (ii) position the switch ineither the first or second position; (iii) set the output level of thevoltage sources; (iv) receive an output signal from the differentialamplifier; and (v) determine at least one parameter of the fluid samplefrom the received output signal.
 11. The system of claim 10, furthercomprising a user interface in communication with the controller. 12.The system of claim 1, wherein the differential amplifier has a built-inoutput offset.
 13. The system of claim 1, wherein the sensor furtherincludes an optical sensor; and the first face of the non-conductivehousing further comprises a lens for emitting light from and receivinglight into the non-conductive housing of the sensor.